Purpose: To utilize standardized procedures to measure the immune response in clinical trials of acellular pertussis vaccine (ACPV). (1) Phase III Trial in Sweden: The following antibodies were measured in 300 sera (150 patients) from the efficacy trial conducted in 1986-87 in Sweden: IgG anti-pertussis toxin (G-PT), filamentous hemagglutinin (G-FHA), fimbriae (G-Fim), and 69K protein (G-69K) by ELISA, IgM anti- lipooligosaccharide (M-LOS) by ELISA, and CHO-cell neutralizing (CHO-NT) antibodies. Examined were pre- and post-immunization sera from 50 children from each of the vaccine groups, JNIH-6 (bivalent PT & FHA), JNIH-7 (monovalent PT), and placebo. Results in the G-PT, G-FHA, and CHO-NT assays were consistent with those published by the Swedish lab. No significant response to Fim, 69K, or LOS was observed in any of the vaccine groups, suggesting that antibodies to these components did not contribute to the clinical protection observed in the trial. (2) Manufacturer-sponsored trials: G-PT and G-FHA were measured in approximately 200 sera from manufacturer-sponsored clinical trials. Results were submitted to the manufacturer for analysis. (3) NIAID-Multicenter Phase II trial: The Laboratory of Pertussis is participating in the analysis of a multicenter trial of ACPV. During the period from Sept. 1990 to April 1991, the laboratory will be receiving approximately 150 sera per week from this study, and on these, the following antibodies will be measured: G-PT, G-Fim, G-69K, and whole-cell agglutination titer. In anticipation of this trial, procedures and reagents have been sent to the NIAID-supported laboratory which will perform the confirmatory testing for this study.